Flies are called flies because, well, they fly! In a specific sense the term "fly" refers to members of the order Diptera. In a more general sense the term "fly" can refer to any flying insect such as may flies, stone flies and others not belonging to this order. The wings of flies are, of course, what they fly with and are thus one of their more important features.

True flies, dipterans, are so called because they have only 2 wings, the second pair being replaced by knoblike structures known as halters which act as stabilizers. Like the wings of most insects, fly wings are covered with tiny hairs which are barely visible at 100X but can be quite clearly seen at 400X. Though appearing to be a dull grey color to the naked eye, these wings reveal interesting colors when seen at higher mangifications.